1. Field of the Invention
The present invention relates to the field of display screen technology. More specifically, embodiments of the present invention relate to flat panel display screens that are useful in conjunction with portable electronic devices.
2. Related Art
As the components required to build a computer system have reduced in size, new categories of computer systems have emerged. One of the new categories of computer systems is the xe2x80x9cpalmtopxe2x80x9d computer system. A palmtop computer system is a computer that is small enough to be held in the hand of a user and can therefore be xe2x80x9cpalm-sized.xe2x80x9d Most palmtop computer systems are used to implement various Personal Information Management (PIM) applications such as an address book, a daily organizer and electronic notepads, to name a few. Palmtop computers with PIM software have been know as Personal Digital Assistants (PDAs). Many PDAs have a small flat display screen associated therewith.
In addition to PDAs, small flat display screens have also been implemented within other portable electronic devices, such as cell phones, electronic pagers, remote control devices and other wireless portable devices.
Liquid crystal display (LCD) technology, as well as other flat panel display technologies, have been used to implement many of the small flat display screens used in portable electronic devices. These display screens contain a matrix of pixels, with each pixel containing subpixels for color displays. Some of the displays, e.g., color displays, use a back lighting element for projecting light through an LCD matrix. Other displays, e.g., black and white, use light reflectivity to create images through the LCD matrix and these displays do not need back lighting elements when used in lit surroundings. Whether color or in black and white, because the displays used in portable electronic devices are relatively small in area, every pixel is typically needed and used by the operating system in order to create displays and present information to the user. Additionally, because the display device is typically integrated together with the other elements of the portable electronic device, the operating systems of the portable electronic devices typically expect the display unit to have a standard pixel dimension, e.g., a standard array of (mxc3x97n) pixels is expected.
FIG. 1A illustrates a typical black and white display screen having a standard size pixel matrix 20 with an exemplary edge-displayed character thereon. The edge-displayed character is the letter xe2x80x9cAxe2x80x9d and is displayed at the left hand side of the display screen at an arbitrary height. The technology could be either transmissive, transflective or reflective passive matrix display, e.g., liquid crystal display (LCD). In a conventional black and white display screen, the background pixels 26 can be light, e.g., not very dark, and the pixels 24 that make up the edge-displayed character can be dark. Importantly, in a positive mode display LCD, unless driven on, the pixels are white. Therefore, the edge location 28 of the display screen, e.g., between the edge of the matrix 20 and the bezel 22 of the portable electronic device, is typically white. As a result, the left edge of the edge-displayed character, xe2x80x9cA,xe2x80x9d has good contrast and is therefore easily viewed by the user. This is the case regardless of the particular edge used, e.g., left, right, top, bottom, because region 28 surrounds the matrix 20.
FIG. 1B illustrates a typical display screen having a pixel matrix 20xe2x80x2 with the same edge-displayed character thereon but using negative mode display LCD technology. In negative mode display LCD, unless driven on, the pixels are black. The edge-displayed character is the letter xe2x80x9cAxe2x80x9d and is displayed at the left hand side of the display screen at an arbitrary height. In this format, the background pixels 26 can still be light and the pixels 24 that make up the edge-displayed character can still be dark. However, importantly, the edge location 28 of the display screen, e.g., between the edge of the matrix 20xe2x80x2 and the bezel 22 of the portable electronic device, is typically dark in negative mode display LCD. Being dark, the edge region 28 is the same or similar color as the pixels 24 that make up the character. Therefore, the left edge of the edge-displayed character, xe2x80x9cA,xe2x80x9d has very poor contrast and is therefore typically lost as illustrated in FIG. 1B. This makes reading the edge displayed character very difficult for a user. This is the case regardless of the particular edge used, e.g., left, right, top, bottom, because region 28 surrounds the matrix 20xe2x80x2.
In an attempt to address this problem, some computer systems do not display edge-located characters to avoid the contrast problems associated with the screen edge. Many desktop computer systems, for example, simply try to avoid the display of edge-located characters on the cathode ray tube (CRT) screen or on a large flat panel display. However, this solution is not acceptable in the case of a small display screen where every pixel is needed for image and information presentation. What is needed is a display that makes maximal use of the available screen pixels while eliminating the problems associated with edge displayed characters in a display format where the pixels of the character are of the same or similar color as the edge region 28. What is also needed is a solution that is also compatible with standard display screen dimensions, formats and driver circuitry. Further, what is needed is a solution that controls the color of border pixels, yet simplifies the design and lowers the cost of displays by reducing and/or eliminating the dependency of border pixel control on separate timing components.
Accordingly, embodiments of the present invention provide an electronic device, e.g., a cell phone, portable computer system, PDA, electronic pager, etc., having a screen that makes maximal use of the available screen pixels while eliminating the problems associated with edge displayed characters in display formats where the pixels of the character are of the same or similar color as the edge region. Embodiments of the present invention are particularly useful in negative mode passive matrix LCD displays that utilize a brighter background and a darker foreground. Embodiments provide the above benefits while being compatible with standard display screen dimensions, formats and driver circuitry. Embodiments of the present invention therefore provide a small display screen with improved viewability, especially at the edge locations. Further, embodiments provide a solution that controls the color of border pixels, yet simplifies the design and lowers the cost of displays by reducing and/or eliminating the dependency of border pixel control on separate timing components. The present invention provides these advantages and others not specifically mentioned above but described in the sections to follow.
A display device is described herein having a display matrix including a pixel border of width x and located around the edge locations of the matrix for improved viewability. In particular, the border region can be several pixels wide, e.g., 1 less than x less than 5. In one embodiment, the border region is two pixels wide and surrounds a display region in which images are generated from a frame buffer memory. In one implementation, both the border region and the display region are implemented using a negative display mode passive display matrix using supertwisted nematic liquid crystal display (LCD) technology. Other passive matrix techniques could also be used in addition to LCD technology, such as, electronic paper, electronic ink, or microelectromechanical machine systems (MEMS), etc.
In one embodiment, the pixels of the border region are controllable between an on state and an off state and have an adjustable threshold voltage level. The threshold voltage level can originate from a gray scale bias circuit which can be controlled by a contrast adjustment. This allows the border brightness and the background brightness to be matched in response to contrast adjustments. In one embodiment, the display screen is a negative mode display in which the pixels are normally black when off. The pixel border is useful in providing contrast in display modes having a white background with black characters displayed therein. In these display modes, the border region is uniformly turned on to provide a white border. As discussed above, the white border adjusts with the background brightness in response to contrast adjustments. The present invention can be applied in either monochrome or color displays. The pixel border is also advantageous in that it can be used with conventional character generation processes of the operating system of the computer used to drive the display screen. In one embodiment, the novel display can be used within a portable computer system or other portable electronic device.
More specifically, an embodiment of the present invention includes a display unit (and a computer system including the display unit) comprising: a passive matrix of independently controllable pixels comprising n rows and m columns of discrete pixels, the passive matrix operable to generate an image in response to electronic signals driven from row and column drivers coupled to the passive matrix, the image representative of information stored in a frame buffer memory; and a pixel border having a predetermined width, the pixel border surrounding the passive matrix and comprising a plurality of pixels which are uniformly controlled between an on and an off state by a common threshold signal.
A display unit is constituted in one embodiment herein by a passive matrix of independently controllable pixels characterized by an active area of n rows and m columns of discrete pixels and a pixel border. In one embodiment, m and n are both 160. The passive matrix is operable to generate an image in response to electronic signals driven from row and column drivers coupled to it, representative of information stored in a frame buffer memory. The pixel border has a predetermined width, and surrounds the passive matrix active area. In one embodiment, the predetermined width is two pixels. The border pixel color state is controlled herein by the frame buffer memory. The pixel border color state is controlled to correspond to information contained in a locus of the frame buffer memory. This locus may be, in various embodiments herein, a single pixel, a row of pixels, or a number of rows of pixels of frame buffer memory. Each row of pixels may be equal to m and/or n, and may be 160. In one embodiment, the frame buffer controls the border pixels directly via a liquid crystal display controller and drivers, without a timing generation mechanism, such as a timing ASIC. In one embodiment, the display unit constitutes a part of a portable electronic device.
In one embodiment, a method of controlling the color of the border pixels constitutes a process including monitoring a locus within the frame buffer memory for information, determining a color for the border pixels corresponding thereto, generating a pixel border color signal corresponding to the color, transferring the pixel border color signal to the liquid crystal display controller, which generates a pixel border color writing signal and impels the drivers to write a color to the border pixels accordingly. The hardware abstraction layer monitors the frame buffer memory locus, determines the border pixel color, and generates the pixel border color signal. In one embodiment, impelling the drivers to write a color to the pixel border does not involve a timing synchronization mechanism external from the hardware abstraction layer.